@JFSM 

For the third Deco, you can try and run an Ethernet cable from it to the second Deco or to the first Deco. Another alternative you can potentially look at is using powerline adapters like the TL-PA7010P KIT to connect Deco units to each other if running an Ethernet cable is not possible.

@Tony 

Thank you for your answer.

I moved recently to this apartment so I am not very familiar with the network setup here.

However, I know that I have a fiber optics modem connected to an Ethernet hub (switch) that goes to all rooms of the apartment through Ethernet.

Since I am using a switch, I would assume that the 3rd Deco should work through cable if connected by Ethernet, using the house's switch. Is my assumption wrong?

The only Deco where I have no way to connect through Ethernet Cable is the 2nd Deco (in the corridor, which is exactly in the middle of the house).

Deco 1 and Deco 3 are on the extreme sides of the house, and I have 1 or 2 Ethernet connections in each room.

Any help here is appreciated.

Many thanks once again.

@JFSM 

If the modem is also a router, that might be an issue.

While the Deco is in router mode, the satellite units need to connect to the main Deco when setting up the Ethernet backhaul, Wi-Fi will take care of itself.

So you need:

modem > Deco 1 > switch > Deco 3

If your Deco is the main router that connecting Deco 3 to the switch will work and will have an Ethernet backhaul to Deco 1. Deco 2 will just connect via Wi-Fi to whichever node presents a better connection.

If the modem is the main router, then you will need to set the Deco in AP Mode. in AP Mode you can wire all the Deco units to the router individually.

So something like:

modem/router > switch > Deco 1

                                         Deco 3

@Tony 

This is very helpful, I was not aware of the differences, and I assumed that each Deco device could be connected by Ethernet and use the cable's full speed, when connected.

In my case, there is a modem/router that looks like this: https://dns.d.pr/relwVX/DHaNKRyanz

Does it make any sense if I disable DHCP and use Deco in router mode?

Or is it better to keep it as it is, and use Deco as AP mode?

If I go with AP mode, does it make any sense to connect each Deco by ethernet (to the router)?

I just want the easiest method (I am not a network guy at all) and to get the best out of each Deco device to give me as close as 250 Mbps as possible.

@JFSM 

I wouldn't mess with the DHCP, which would likely create headaches.

I would see wanting router mode if you want the features such as parental controls, antivirus, like this article describes: tp-link.com/us/support/faq/2399/

If the main objective is speed, then I would keep the Deco in AP mode, and wire them to the router or to the switch.

@Tony 

those are good suggestions. 
 

Right now, I've reconfigured the network as AP and re-added the Decos after resetting them (starting fresh).

The problem I am facing now is that the 3rd satellite Deco (connected by Ethernet to the wall - switch - modem) is showing with a red light now. It was fine when I added it to the network but I believe it is quite far away now from the main deco hence not getting enough signal.

Is this important? Do they all need to be linked together wirelessly?

I'm starting to think that this mesh solution is not exactly what I thought it was. I thought satelite 2 would connect to the main deco, and satelite 3 would connect to the nearest one (main or second satelite) like a range extender kind of.

is there a better solution (with new WiFi devices if needed) to get one single WiFi network but with a cable connection on each WiFi device? 

@JFSM 

If the Deco was wired then it should not be red. If the Deco is red then it may be too far via Wi-Fi, but that should not factor in since you are using a wired connection. Take that Deco to the main Deco, and connect an Ethernet cable. The Deco should turn red, but then turn green. If that works, there may be something with the cable or switch?